The brain as an organ of mind . rilla seems tobe due principally to thegreater development init of the lower part ofthe parietal region of theHemispheres. Thus, thegreat size of the supra-marginal lobule and ofthe lower part of the as-cending parietal convo-lution, seems to causethe lower half of thefissure of Rolando to bepushed decidedly for-wards. These peculiari-ties do not appear to Fig IIS.—Brain of Crang, view of base or bflVP hpPT) nvPvinncilv ^^ ^P^^^- C^^en, after Tiedemann.) Deen pi e^ lOU Sn ^^,^^,^ ^.^^^ ^^^^ ^^ Human Brain Fig. 144. noticed by anatomists. The External
The brain as an organ of mind . rilla seems tobe due principally to thegreater development init of the lower part ofthe parietal region of theHemispheres. Thus, thegreat size of the supra-marginal lobule and ofthe lower part of the as-cending parietal convo-lution, seems to causethe lower half of thefissure of Rolando to bepushed decidedly for-wards. These peculiari-ties do not appear to Fig IIS.—Brain of Crang, view of base or bflVP hpPT) nvPvinncilv ^^ ^P^^^- C^^en, after Tiedemann.) Deen pi e^ lOU Sn ^^,^^,^ ^.^^^ ^^^^ ^^ Human Brain Fig. 144. noticed by anatomists. The External Perpendicular Fissure is particularlywell marked in the Chimpanzee (fig. 115), though it isseldom distinctly visible in the human brain. In theChimpanzee it is not crossed by any superficial bridgingconvolutions, so that its posterior border (or Operculum as it is called in lower forms of Quadrumana) is uninter-rupted. This fissure is continued on the inner side of thebrain as the Internal Perpendicular Fissure (fig. 120,/p).. 300 THE BRAIN OF QUADRUMANA. * bridging which In the Gorilla also, the External Perpendicular Fissure(fig. 117, s c) is very distinct and long, its hinder margin(Operculum) being convex anteriorly, and somewhat moresinuous than it is in the Chimpanzee. The first bridgingconvolution emerges from beneath it above. But in theOrang this Perpendicular Fissure is sometimes muchshorter and less obvious (fig. 119) than it is in either ofthe other two great Apes, so that in this respect its brainapproaches more closely to that of Man. It is sometimes interrupted above byan upperconvolutionhas a superficial posi-tion of this kind inno other of the Quad-rtimana, excei:)t inAteles. According to Ptolle-ston this superficialposition of the upperor first bridging con-volution is not con-stant in the Orang or Fig. 119.—Brain of Orang, upper aspect. (Duncan, eVCU in Man while in both it may attimes be present onone side and absent on the other. He adds :— In thehigh
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